Well, looks like I have to wait for it to come on again. I called the Ford dealer to set up an appointment, and they said that Ford won't pay for it unless the light is on because I'm passed the bumper to bumper waranty, and into the 100k powertrain. She said I could still bring it in, but unless the tech could find something wrong with it (they probably wouldn't since the light isn't on, and there is no loss of power), I would be charged for the diagnostic.
Also, I didn't realize that there is a $100 deductible on the powertrain waranty. Wasn't real pleased to find that out, but I guess it's in the fine print somewhere. I'm mainly worried about having to pay multiple times when they don't fix the problem the first time (because they probably won't).